1. Field of the Invention
This invention relates to a hydrogen storage alloy powder, and more particularly, to an improved hydrogen storage alloy powder adapted for use as a negative electrode of nickel-hydrogen secondary cells. The invention also relates to an electrode made of such a hydrogen storage alloy powder and exhibiting good low temperature and high-rate discharge characteristics.
2. Description of the Prior Art
After the discovery of hydrogen storage alloys capable of storing or occluding and releasing hydrogen, they have had wide utility not only in the field of hydrogen storage, but also in the field of cells or batteries. Especially, their application to alkaline secondary cells has now been put into practice, and successive improvements of hydrogen storage alloys have been made therefor.
For instance, a LaNi.sub.5 alloy, which was initially developed and has a CaCu.sub.5 crystal structure, has been improved by replacing part of La with a rare earth element such as Ce, Pr, Nd or the like and part of Ni with a metal element such as Al, Co, Mn or the like, thereby realizing a higher capacity and a longer life of the alloy.
However, where it is intended to improve a discharge capacity at temperatures of 0.degree. C. or below, there is the tendency that the life of an electrode using such an alloy is shortened. Thus, it has been very difficult to obtain a nickel-hydrogen secondary cell whose negative electrode has both good low temperature characteristics and long life. Moreover, these alloys are not satisfactory with respect to a high-rate discharge characteristic. Thus, nickel-hydrogen secondary cells having a satisfactory high-rate discharge characteristic have never been known in the art.